Universal amplified telephone handset

Abstract

An amplified telephone handset includes a current sensing circuit that senses the polarity of DC voltage supplied from a telephone base, irrespective of whether the DC voltage is of standard or reverse polarity. This feature allows the amplified telephone handset to operate with telephone bases that supply voltages through a telephone cord of either standard or reverse polarity. The amplified telephone handset also includes a voltage detection circuit that detects "off-hook" or "on-hook" states by detecting the absence or presence of the voltage. If a DC voltage is detected, then the amplified telephone handset is coupled to the telephone base and the voltage detection circuit disconnects the battery from receiver and transmitter circuits in the amplified telephone handset, placing the amplified telephone handset in a "on-hook" state. Conversely, when the amplified telephone handset is removed from the telephone base and no charging voltage is present, the voltage detection circuit connects the battery to the receiver and transmitter circuits in the amplified telephone handset, placing the amplified telephone handset in the "off-hook" state. An LED indicator on the amplified telephone handset indicates the level of electrical charge of the battery by the intensity of the LED diode.

We claim: 
     
       1. An amplified telephone handset coupled to a telephone base via a telephone connector, the handset comprising: a receiver amplifier electrically coupled to the telephone base to receive telephone signals via the telephone connector, for amplifying the received signals;   a transducer coupled to the receiver amplifier to produce the amplified signals;   an electrical storage device electrically coupled to the receiver amplifier for providing electrical power thereto; and   a current sensing circuit having electrodes coupled to the telephone connector and receiving therefrom a standard polarity voltage signal or a reverse polarity voltage signal, the current sensing circuit having a first subcircuit for receiving the standard polarity voltage signal and a second subcircuit for receiving the reverse polarity voltage signal, each subcircuit producing a respective voltage signal in a mutually exclusive manner to couple the electrical storage device to the receiver amplifier.   
     
     
       2. The amplified telephone handset of claim 1 further comprising: a voltage detection circuit coupled between the current sensing circuit and the electrical storage device, having a first state disconnecting the electrical storage device from the receiver amplifier in response to the absence of either the standard polarity voltage signal or the reverse polarity voltage signal, and a second state connecting the electrical storage device to the receiver amplifier in response to the presence of either the standard polarity voltage signal or the reverse polarity voltage signal.   
     
     
       3. The amplified telephone handset of claim 2 wherein the current sensing circuit further comprises: a first transistor having a first terminal, a second terminal, and a third terminal; and   a second transistor having a fourth terminal connected to the first terminal of the first transistor, having a fifth terminal connected to the first terminal of the first transistor, and having a third terminal connected to a common node of the third terminal of the first transistor and the voltage detection circuit.   
     
     
       4. The amplified telephone handset of claim 2 wherein the current sensing circuit further comprises: a full-wave diode-bridge rectifier having inputs for receiving the standard polarity voltage signal or the reverse polarity voltage signal, and having a first output for supplying the standard polarity, voltage signal to the voltage detection circuit and having a second output for supplying the reverse polarity voltage signal to the voltage detection circuit.   
     
     
       5. In a system including an amplified telephone handset having a battery, and a telephone base supplying a voltage signal having a standard or a reverse polarity through a telephone connector to the handset, a method of operating the amplified telephone handset to cooperate with the telephone base, comprising the steps of: sensing in the amplified telephone handset the presence of the voltage signal from the telephone base;   responsive to the standard polarity of the voltage signal, supplying the voltage signal of standard polarity to the battery; and,   responsive to the reverse polarity of the voltage signal, supplying the voltage signal of the reverse polarity to the battery.   
     
     
       6. The method of claim 5 wherein the amplified telephone handset is comprised of a transmitter circuit and a receiver circuit, each circuit coupled to the battery and receiving power therefrom, the method further comprising the steps of: responsive to the presence of a voltage signal, connecting the battery to the transmitter and the receiver circuits; and   responsive to the absence of the voltage signal, disconnecting the battery from the transmitter and receiver circuits of the amplified telephone handset.   
     
     
       7. The method of claim 5 further comprising the step of: responsive to the absence of the voltage signal, disconnecting the battery from the receiver amplifier circuit.   
     
     
       8. In a system including an amplified telephone handset having a battery, a receiver amplifier circuit coupled to the battery and receiving power therefrom, and a telephone base supplying a voltage signal having a standard or a reverse polarity to the handset, a method of operating the amplified telephone handset to cooperate with the telephone base comprising the steps of: sensing in the amplified telephone handset a presence or an absence of the voltage signal from the telephone base;   responsive to the presence of the voltage signal, detecting whether the voltage signal is the standard polarity voltage signal or the reverse polarity voltage signal;   coupling the battery to the receiver amplifier circuit if the detected voltage signal is the standard polarity voltage signal; and   coupling the battery to the receiver amplifier circuit if the detected voltage signal is the reverse polarity voltage signal.